1. Field of the Invention
This invention relates to a process for forming a tungsten silicide layer on an integrated circuit structure of a semiconductor wafer, and more particularly, it relates to the treatment of a susceptor, having an aluminum nitride surface thereon, used in forming the tungsten silicide layer on the semiconductor wafer.
2. Description of the Related Art
In the formation of integrated circuit structures on semiconductor wafers, a vacuum chamber is provided having a susceptor on which the wafer is mounted during deposition of various layers on the wafer. When a material such as tungsten silicide is deposited, the temperature for deposition can range from about 500.degree. C. to as much as 700.degree. C. This temperature range requires the use of a susceptor fabricated from aluminum nitride or aluminum nitride-coated graphite to withstand the higher temperatures.
However, when a material such as tungsten silicide, for example, is deposited on a number or series of wafers, the inside walls or surfaces of the vacuum chamber become coated with tungsten silicide. This coating has to be removed periodically to prevent its flaking off and contaminating the integrated circuit structure. The removal of a coating of tungsten silicide may be accomplished by the use of a fluorine-containing etchant such as NF.sub.3 or C.sub.2 F.sub.6 gas. Normally, the cleaning of the vacuum chamber is performed using a plasma in conjunction with the fluorine-containing etchant gases. However, after such a cleaning treatment, the initial wafer subsequently mounted on the susceptor is not adequately receptive to the deposition of a layer of tungsten silicide. Thus, the initial or first wafer treated after cleaning is of inferior quality and is rejected. This, of course, is not only a rejection or loss of the cost of the tungsten silicide layer but also is a rejection or loss of the whole integrated circuit structure created to that point. It will be seen that the loss is not insubstantial. If the vacuum chamber is cleaned, for example, after every tenth wafer treated with tungsten silicide, the number of wafers rejected can amount to ten percent.
Thus, it would be very desirable, particularly because of economics, to eliminate the inferior deposition of tungsten silicide on the first or initial wafer after such a lo cleaning of the vacuum chamber.